Desalting of hydrocarbon oils



N. L. DlcKlNsoN DESALTING 01? HYDROCARBON OILS- Filed Dec. 29, 1943 sept. 3, 1946.

' In vemdr: l Norman L. Dickinson Afforney i V BSN Patented Sept. 3, i946 2,406,748 Y nnsAL'rrNG oF HrDRocanBoN oiLs lNorman L. Dickinson, Baskng Ridge, N. J., as-

signor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application Decembei 29, 1943, serial No. 516,057

Claims.

. 1 A This invention relates to the desalting of hydrocarbon oils and it pertains more particularly to the desalting of reduced crudes for the preparation of charging stock to catalytic cracking procextremely important consideration in catalytic conversion processes and the frequent replacei ment of catalyst because of salt contamination Would be economically prohibitive.

The problem of removing salt from crude peesses. 5

Many crude petroleum oils contain large troleum oils has confronted the industry from its amounts of salts, particularly sodium chloride, very beginning and enormous amounts of recalcium chloride and magnesium chloride. The search have been conducted in an effort to solve amount Voi such salts varies with the crudes, Some this problem. Numerous processes have been procrudes containing only traces of salt, others conposed and some of them used with varying detaining about .0l to .2 pound per barrel and some grees ofsuccess but all of them are expensive containing as much as 5 pounds or more per barand for the most part they do not reduce the rel.` Thesalt content of typical Mid-Continent salt content to the extent suliicient for charging crudes is usuallyV within the approximate range stocks in catalytic cracking processes. An object of .04 to .l5 pound per barrel. Since thisr salt is 15 of my invention is to provide an improved method largely concentrated in the residuum on distillaand means for removing salt from oils and partion and the residuum or reduced crude is fre'- ticularly from reduced .crudes which method will quently 50% to 15% of the total crude it will be be characterized by lower capital investment costs seen that the amount of salt in the residuum may and operating costs than any processes heretofore range from about 0.1 to `1 pound per barrel even 20 known. A further object is to obtain higher yields in the case of Mid-Continent crudes and may be of desalted charging stocks from reduced crudes from .5 to 5 or more pounds per barrel in the case than could be obtained by any other known'procof crudes initially higher in quantities of salt. ess. A further object is to provide a desalted An object of my invention is to provide an imcharging stock of higher quality and specically proved method and means forremoving salt from to avoid the existence of cracking conditions in such oils and particularly from such reduced the desalting ystep so that no low octane number crudes. gasoline will be produced and so that the value The salt removal problem is particularly aggraof the charging stock will not be otherwise imvating in the preparation of charging stocks for paired. catalytic cracking processes. Heretofore catalytic A further object is to remove along with the cracking has been eiected only on distillate oils salt certain high molecular Weight substances or the vaporizable portions of reduced crudes. It which are deleterious' in catalytic cracking operis impossible'to effect complete vaporization of reations but which may serve a useful purpose for duced crudes Without carbonization and if such other uses even in the presence of removed salt. vaporization is effected by thermal means it re- Other objects Will be apparent as the detailed 'suits in the production of loW boiling oils of undescription of the invention proceeds. desirably low knock rating, i. e. gasolines having I have discovered that when a reduced crude of an A. S. T. M. octane number of the order of 55 high salt content is admixed With propane in to 60. In order to vavoid this undesirable thermal k amounts of about 3 to 5 liquid volumes of propane cracking oi residual cracking stocks it has been 40 per volume of reduced crude, heated to a temproposed to inject these stocks directly into a perature Within the approximate range of 140jto catalytic cracking reactor to'which the necessary 185 F. under sufcient pressure to prevent vaheat for conversion is supplied by other means. porization of the propane, and introduced into an Provision can be made for burning the additional `eiiicient settling zone which is likewise maincarbonaceous deposits which are laid down in tained under sufficient pressure to prevent prosuch operations but the accumulation on the catpane vaporization, the salt can be carried out of alyst of inorganic salts from salt-bearing oils the solution With other propane insoluble materuins the catalysts. An object of my invention rials which are present in the reduced crude and is t0 provide a method and means for the cata- Withdrawn as a separate stream from the base of lytic cracking of such heavy reduced crudes of the settling zone. While propane is the preferred high salt content Without formation of low antisettling agent for this desalting operation, other knock gasolines and without deleteriously afiectnormally gaseous hydrocarbons or mixtures ing the .activity of the catalyst.r The importance thereof may be employed, higher temperatures of safeguarding catalyst activity can not be overand lower pressures being used in the case of bu- 'emphasized because the cost of the catalyst isan 55 tane and lower temperatures and higher pressures 3 in the case of ethane. The normally gaseous hydrocarbons should preferably be saturated although the presence of oleflns is not as objectionable in this process as in the process for producing lubricating oils by conventional propane deasphalting methods. The amount of normally gaseous hydrocarbon employed should be Within rather closely deiined limits which in the case of propane are from 3 to 5 volumes, about 4 volumes per volume of reduced crude being preferred. The high propane-to-oil ratios employed in propane deresining processes for lubricating oil manufacture are unnecessary and undesirable in the propane desalting operation, and the reduced crudes for desalting are usually not of the same type as those used for the manufacture `oi lubrieating oils. The invention will be more clearly understood from the following descriptionbf a 14,250 barrel per stream day deasphalting plant employed for the preparation from a salt-bearing reduced crude of a charging stock for a iluid catalytic cracking system.

The accompanying drawing which forms a part `of .this specification is a diagrammatic ilow sheet of a commercial desalting plant,

Any salt-bearing reduced crude may be employed as a charge to the system, examples being an 18.7 A. P. I. East Texas-Magnolia reduced crude, a 21.2 A. P. I. gravity South Louisiana reduced crude, a 16.2 A. P. I. gravity New Mexico reduced crude, etc. These reduced crudes are preferably about to 30% of the total crude and their salt contents may range from .05 to 1, usually from .1 to .5 pound per barrel. Such charge is introduced from source l0 at a temperature of about 200 F.

The propane in this example is a technical grade which may contain about 1 to 3% oi ethane and small amounts of isobutane and butane. The word propane is used herein and in the accompanying claims is intended to mean a normally gaseous hydrocarbon of substantially the characteristics of propane, i. e., to include mixtures of propane with small amounts of other normally gaseous hydrocarbons. The propane is `stored in tank II at a temperature of about 120o F. and a pressureof about 255 pounds per square inch (all pressures being gauge pressures).

y57,000 barrels per day or 424,000 pounds per hour to line I6. If desired of course separate pumpsmay be used for introducing charge and in fact one charging stock may be treated in one portion of my system while another charging stock is being treated in another part. The propanecharging stock streams from lines I4 and I6 are raised from a temperat-ure of 137 F. to 185 F. by steamheaters and 20', and at this temperature the mixture is introduced through lines 2| and 2 I into settlers 22 and 22' which are designed to operate at a temperature of 185 F. and a pressure of 525 pounds per square inch. These settlers are preferably large cylindrical tanks mounted at a slight angle to the horizontal and they are preferably provided `with sloping lbaffles at intervals of or 4 inches, the slope of the baiiies being Y about 45 degrees. The charge to the settlers is distributed in streams flowing between these baflles so that the baffles do not impede flow but do avoid possible turbulence and provide surfaces on which settled droplets may coalesce and run 5 down to the base of the settler without interfering with the settling operation. By using such sloping baliles each particle only has to settle a few inches before it is coalesced on one of the collecting plates and thus effectively removed from the solution. Any eflicient type of settler may be used but the sloping baille type hereinabove described has been found to be very efcient and to give excellent results.

The salt is entrained or carried by the heavy materials which settle out in settlers 22 and 22 and these settled liquids are withdrawn through lines 23 and 23. The relatively salt-free propane solution is removed from the opposite side of the settler and preferably from the top thereof through lines 24 and 24. These solutions pass through pressure reducing valves 25 and 25 wherein the pressure is reduced to approximately 280 pounds and the temperature reduced to approximately 136 F. Each of the salt-free streams after the pressure reducing step will contain about 82,300 pounds per hour of oil, 122,500 pounds per hour of liquid propane, 85,500 pounds of propane vapor. These streams are then introduced by lines 29 and 26 into depropanizers 21 and 21 Which operate at about 180 F. and about 280 pounds gauge. pressure. The depropanizers are heated by steam coils 28 and 28. About 182,400 pounds per hour of propane vapor is removed from the top of these depropanizers through line 29 and line 29', this propane being returned through back pressure valve 30, line 3I and condenser system 32 and finally returned at a temperature of about 120 F. to storage tank I I.

The liquid stream which flows over bales 33 and 33 is Withdrawn in amounts regulated by liquid level control valves 34 and 3'4 through lines 35 and 35 to depropanizers 36 and 36. These depropanizers are likewise heated by steam coils 37 and 37 `for maintaining a temperature of about 260 F. and a pressure of about 270 pounds gauge. About 15,650 pounds per hour of propane vapor is withdrawn from the top of depropanizers 36 and 36 through lines 38 and 38', this propane vapor then being passed through lines 39 and 40 to line 3 I, condensed system 32 and storage tank II.

The liquid which flows over baffles 4I and 4I is then Withdrawn in amounts regulated by liquid level control valves 42 and 42 and introduced through line 43 to desalted oil stripping tower 44.

About 164,600 pounds per hour of oil containing about 13,900 pounds per hour of propane is thus charged to the stripper which is maintained at a temperature of about 250 F. and a pressure of about 5 pounds gauge. Live steam is introduced through line 45 for stripping the propane from the oil, the propane and steam being taken overhead through lines 46 and 41 to jet condenser 48 for condensation of the stripping steam.

Desalted oil is withdrawn from the base of stripper 44 through line 49 by pump 5I) which operates to maintain a constant liquid level in the lower part of the stripper, The desalted oil amounts to about 12,350 barrels per stream day and it is substantially free from salt. Thus a charging stock which contains .35 pound of salt per barrel can be desalted in this system so effectively that the salt content on the finished oil Willbe less than .0017 pound per barrel which is less than l/zou of the amount of salt in the original charge and is so small as to be prac# tically negligible. L

The heavy liquid containing salt may be passed from lines 2'3 and 23 thru coils 5l and 5I' in furnace 52 and'heated from an entering'temperature of about 185 F. to a transfer line temperature of about 400 F. The streams are then combined and introduced by line 53 into flash or vapor separation drum 5d Vwhich is operated at a ternperature of about 400 F. and pressure of about 270 pounds per square inch. Propane vapor is withdrawn from the top of this drum at the rate of about'l3,300 lbs. per hour and conveyed by line 55 to lines 4'0- and 3! for condensation and return tostorage drum il.

The remaining salt-containing liquid, about 29,400 pounds per hour of salt plus heavy components from the reduced crude, and about 700 pounds per hour of liquid propane, is withdrawn through line 56, through liquid lever controlled valve 5T and introduced into stripper 58 which operates at about 400 F. and about 5 pounds per square inch pressure. Live steam is introduced through line 59' and the stripped propane and steam is taken overhead through lines 59 and 41T to jet condenser 48. Water is introduced into jet condenser 48 which isr operated at about 2 pounds per square inch pressure. Water is introduced into the jet condenser through line bi' at about 85 F. and this water together with condensedA steam is removed from thel base of the jet condenser at about 110 F. through linev 62. The overhead which consists of about 14,600 pounds per hour of propane vapor is passed by line VE33 to trapout drum 04 which is operated at about l pound pressure and about 100 F., any aqueous condensate being removed through line 65. Propane vapor from the top of this trap is passed by line 65 to compressor 66- and thence by lines 6l and 3l back to the condenser system and propane storage drum.

The depropanized material leaves the base of stripper 53 through line 68, pump 63 maintaining a constant liquid level inthe lower part of stripper 53.

The desaltedVv oil removed through line 49 is excellent charging stock for catalytic cracking processes and particularly for processes employing the so-called' huid-type operation although it may be used as charging stock for fixed bed units of the Houdry'type or moving bed units which are commonly known to the art as the Thermofor" catalytic (process. The catalysts employed in all of-these processes is of substantially the same type and in all cases it is essential that the charging stock be substantially free from salt. The catalytic cracking may be effected with catalysts of the so-called natural or clay type which is an acid treated or activated Bentonite or Montmorillonitek clay or it may be a synthetic silica-alumina or synthetic silica-magnesia catalyst.

A suitable catalyst may be prepared by ball milling silica hydrogel with alumina or magnesia using 2' to 30%, for example about 15% of alumina or magnesia, the ball-milled dough being dried at aV temperature of about 240 F. and then activated by heating to a temperature of about 900l to 1000 F. Alternatively, the catalyst may be prepared by Aforming a gel from dilute sodium silicate in the presence of an aluminum salt by the addition of excess sulfuric acid, boiling the resulting gel for an hour or two with an excess of dilutey ammonium hydroxide solution, wash-` ing', drying and heating as in the previous examlyst.

ple. The catalyst may be rendered more stable at high temperatures by the addition thereto of zirconia, aluminum Vfluosilicate or other stabilizer.

The catalytic cracking is effected at a temperature within the approximate range of '750 to 1050 F., preferably about 900 to 950 F., e. g. about 925 F. The pressure at which catalytic cracking is eifected may be of the order of atmospheric to 50 pounds or more per square inch, preferably about 5 to 15 pounds per square inch, e. g. about 10 pounds per square inch (gauge pressure in all cases). The flow rate or time of contact Will depend somewhat upon the catalyst, charging stock, and system employed and in a fixed or a moving bed system it may be within the approximate range of .3 to 3, for example about l volume of liquid charge per hour per volume of catalyst in the reactor with an onstream within the general` vicinity of 10 to 30 minutesl or more. In the fluid-type or powdered catalyst vsystem' the catalyst-to-oil weight ratio in the stream entering the "reactor may range from about 1:1 to 25:1 and the Weight space velocity in the reactor itself may be within the approximate range of .3 to 3 pounds of charging stock per hour per pound of catalyst in the reactor.

The catalyst is periodically regenerated by combustion of carbonaceous deposits therefrom usually at temperatures within the approximate range of 950 to 1150 F., care being taken tok avoid unduly high temperatures. The heat of combustion may be vemployed for preheating and/or vaperizing charging stock as well a-s for supplying at least a part of the endothermic heat of cracking. When salt-bearing reduced crudes are employed as charging stock there is not only excessively large amounts of carbonaceous material deposited on the catalyst but there is also a deposit of salt on the catalyst and this salt deactivates the catalyst in a relatively short time and makes it necessary for the entire catalyst to bel discarded. Since the cost of the catalyst is one of the most important items in catalytic cracking processes, it is essential that this catalyst poisoning be avoided. Heretofore salt-bearing reduced crudes could not be used as charging stocks and when overhead fractions were taken therefrom said fractions resulted in undesirably low yields of products characterized Vby undesirably low octane numbers. My invention makes possible a substantial increase in the total amount of high octane number motor fuel obtainable from such reduced crudes andv at the same time it makes possible the use of salt-bearing crudes without rapidly deteriorating'or ruining the cata- My process is particularly advantageous for reduced crudes containing upwards of about .1

pound of salt per barrel of reduced crude and it is advantageous on charging stocks containing only .05 pound per barrel or as low as .0l pound per barrel. The salt content is substantially eliminated by my process so that desalted oils are obtained in which the salt content is less than .005 pound per barrel and is usually less than .002 pound per barrel. At the same time I remove from the charging stock the high molecular weight components which are objectionable in the catalytic cracking charge but may be very useful for other purposes. Y

The reduced crudes are preferably about 10 to 30% of the total crude and are thus substantially free from hydrocarbons of low or intermediate boiling range. The A. P. I. gravities of such re- 7, duced crudes may be within the approximate range of 15 to 25 although beneficial results may be obtained on stocks of higher or lower gravities.

While specific operating conditions have been described in connection with the particular example hereinabove set forth, it should be understood that operating conditions will vary for different stocks processed and that various modications and alternativesl may be employed both with regard to the operating system and to the conditions employed therein. I have found that the salt can be almost completely removed from the solution in the settling drum regardless of the amount of heavy materials, asphaltic materials and the like which may be separated and removed therewith. Simultaneously with the desalting I may therefore effect varying degrees of deasphalting. The effect of propane ratio on the amount of asphalt precipitated depends to some extent upon the nature of the reduced crude but usually has the effect of decreasing the amount of asphalt as the propane ratio is increased. On very short heavy reduced crudes, increasing the propane ratio in the range between 3:1 to 5:1 may have the elect of increasing the asphalt Iwhereas a further increase above 5:1 tends to decrease the amount of asphalt. My desalting plant is not designed with the idea of having propane-to-oil ratio as a controllable variable, but it is well to understand what can be expected to occur if the propane ratio does vary.

Operating temperature on the settling system within the limits for which the plant is designed is intended as a controllable variable and has a denite effect upon the amount of asphalt precipitated. Contrary to the usual solution laws an increase in temperatures causes a decrease in the solubility of asphalt and thus increase in the amount of asphalt precipitated. With a given type of reduced crude and a given propane ratio, the higher the settling temperature the greater will be the amount of asphalt separated.

The range of temperature in the settling vessels may vary Within the approximate limits of 140 to 185 F., 140 F. giving minimum asphalt production and 185 F. giving maximum asphalt production which is usually desired along with the desalting of the reduced crude.

It is essential that the propane be kept in liquid condition in the settling zone since the vaporization of any propane in the settlers Iwill prevent proper settling of the lower phase and thus interfere with the desired desalting operation. Usually a reasonable pressure on the settling Zone is maintained above the amount calculated for complete liquid phase conditions and it is important in determining the pressure to take into account any small amounts of ethane that may be present in the propane. With the exception of the two strippers and the jet condenser the pressures employed at various stages following the settlers are controlled primarily by the pressure maintained on the propane storage tank. The high pressure ashpropane recovery units can be said to float on the propane storage tank, i. e. to carry such pressure as is necessary to make the vapors from these vessels move through the lines and condensers back to the storage tank. The pressure on the two strippers and on the jet condenser is reduced to atmospheric pressure in order to facilitate complete vaporization of propane and the propane thus released is compressed for return to the condenser and sto-rage system.

As above stated, my invention is not limited to the precise system and conditions hereinabove described.' The salt may be separated from the solution of oil in normally gaseous diluent by means of centrifuges or other separation means. The diluent may be recovered in other manners, and in fact at least a part of the diluent may be left in the oil which is charged to the catalytic cracking system. The invention is particularly applicable to salt-bearing reduced crudes which are not satisfactory for the manufacture of lubrieating oils but are to be used as cracking stocks for gasoline manufacture. Outstanding features of the invention are the low construction and operating costs, the remarkable effectiveness of the salt removal, and the increased yields of high octane number cracked gasoline that are obtainable from any given reduced crude without deleterious eifect on the catalyst employed in the cracking operation.

I claim:

1. The method of desalting reduced crude which comprises maintaining a quantity of propane in storage at a temperature of about F., pumping about 4 volumes of propane from said storage and about 1 volume of a salt-bear ing reduced crude through a heating Zone to increase the temperature of the mixture to at least about F. but not more than about 185 F., introducing the heated solution into a settling zone maintained at a temperature Within the approximate range of 140 to 185 F. and under a pressure suniciently high to prevent vaporization, separating the salt together with undissolved high molecular weight components of the reduced cruded from the propane solution of dissolved components in the settling zone, removing the solution from the settling zone, reducing the pressure on the withdrawn solution but maintaining the reduced pressure higher than propane storage pressure, heating said solution for vaporizing propane therefrom, condensing said vaporized propane and returning it to said storage, reducing the pressure on the remaining propane solution to approximately 5 pounds per square inch, stripping said solution with steam for removing propane therefrom, condensing the stripping steam with a jet of relatively cool Water, separating water from propane vapors, compressing, condensing and returning said propane vapors to said propane storage.

2. The method of desalting a reduced crude which comprises main-taining a quantity of propane in storage at elevated pressure and at an elevated temperature which is substantially below about 140 F., mixing about 3 to 5 volumes of propane from said storage with about 1 volume of a salt-bearing reduced crude, heating said mixture and holding it in a settling zone at a temperature within the range of about 140 to 185 F. under a pressure sufficiently high to prevent vaporization for a time sumcient to effect separation of salt together with undissolved high molecular weight components of the reduced crude from the propane solution of dissolved components in the settling zone, removing the solution from the settling zone, reducing 4the pressure on the withdrawn solution but maintaining the reduced pressure higher than the propane storage pressure, heating said solution for vaporlzing propane therefrom, condensing said vaporized propane and returning it without compression to said storage, reducing the pressure on the remaining propane solution to a level from about atmospheric to about 5 pounds per square inch gauge, stripping said solution at the reduced pressure with steam for removing propane there'- pound of salt per barrel.

5. The method of claim 2 which includes the steps of passing separated salt and undissolved high molecular Weight components of the reduced crude together with propane associated therewith from the settling zone to a heating zone, heating said materials to atemperature of lapproximately 400 F., separating propane vapors from the heated materials at a pressure which is higher than the propane storage pressure, condensing the separated vapors and returning them to said propane storage, reducing the pressure of the remaining materials to about atmospheric to about 5 pounds per square inch, stripping said materials with steam at said reduced pressure for removing residual propane vapors, condensing and separating steam from said residual propane vapors and compressing, condensing and returning said propane vapors to said propane storage.

NORMAN L. DICKINSON. 

